[Unilateral hyperlucent lung].

We report a case of 33 year old man who consulted us in 1994 for recurrent bronchitis sometimes with haemoptysis. The physical examination was unremarkable. At consultation abnormal fascicular sounds were noted at the left base. A chest x-ray showed hyperlucency of the left lung associated with a very small left hilar shadow. We considered the diagnosis of Mac Leod's syndrome after eliminating a proximal obstructive pathology and pulmonary embolus. Mac Leod's syndrome or Swyer James' syndrome was described in 1954 and is suggested on the standard radiograph above all if the expiratory films have confirmed the presence of air trapping. Angiography shows a slender and fine pulmonary network. Computer tomographic examination of the chest rules out a bronchial tumour, excludes bullous emphysema and reveals hyperlucent zones. Scintigraphy with ventilation perfusion supplies the essentials to understanding the mechanism (a syndrome of aerated lung which is neither directly ventilated nor perfused). The expiratory function tests most often show a restrictive syndrome but sometimes an obstructive syndrome is found with associated air trapping. The disorder does not progress and the prognosis is good.